VITAMINS 



359 



CH3- 



CH3 



-tocoplierol 



CH3 



R 



HO- 



CH3 



5-tocopherol 



CH, 



-R 



R stands lor the side chain ol a-tocopherol. These four forms of 

 vitamin E thus differ only in the number of methyl groups on the 

 aromatic ring. 



In vitro the tocopherols are good antioxidants and retard develop- 

 ment of rancidity in fats by preventing the aerobic autoxidation of the 

 carbon chains of unsaturated fatty acids. Vitamin concentrates are 

 used to some extent in foods to prevent the development of the flavors 

 and odors characteristic of oxidative rancidity. Synthetic antioxidants 

 administered to deficient animals cure most of their deficiency symp- 

 toms, so vitamin E is thought to function in animals primarily but 

 perhaps not exclusively as an antioxidant. 



Vitamin E is known to be required by all the laboratory and 

 domestic animals studied. Presumably it is required by man as well, 

 but there is no direct evidence. Reliable estimates of daily allowances 

 are not yet available and perhaps not of practical importance, since 

 the amounts in ordinary foods and feeds seem quite adequate. Wheat- 

 germ oil, cottonseed oil, and soybean oil are rich sources with small 

 amounts in meat, milk, eggs, leafy plants, and some fruits. 



Deficiencies in himian beings are not definitely known and probably 

 are very rare. Likewise they are probably rare in animals outside 

 the laboratory. Herbivores may be slight!) more prone to deficiency 

 symptoms, for they are more sensitive than are other animals to spe- 

 cial diets in the laboratory. Deficiency symptoms inider experimental 

 conditions are reproductive failures, including poor hatchability of 

 eggs, kidney lesions, and muscular distrophy. Addition of vitamin E 

 to the diet reverses early stages of these changes but has little effect 

 on the miscarriages, abortions, sterility, and muscle degenerations 

 commonly encountered in animals on natural diets. Presumably these 

 same symptoms also arise from other causes than deficiency of to- 

 copherols. 



VITAMIN K 



Two forms of this vitamin have been isolated and many more 

 active substances have been synthesized. Most of these are naph- 



